A physically unclonable function (PUF) refers to a physical structure that is embodied in a physical device. Today, PUFs are usually implemented in integrated circuits and are typically used in applications with high security requirements. Static random access memory (SRAM) PUF is an example of such technology that is becoming popular. A PUF device is easy to evaluate but hard to predict or clone due to the way it is constructed based on the inherent process variations of devices. As a result, a PUF device is easy to make but practically impossible to duplicate, even given the exact manufacturing process that produced it. In this respect it is the hardware analog of a one-way function.